Production of alicyclic carboxylic acids



Patented Nov. 23, 1948 UNITED STATES PATENT orrics signer to said Sowa No Drawing. Application my 15,-1946,' Serial No. 670,018

This application a Our invention relates to methods for conducting reactions between conjugated dienes and 1,2 unsaturated carboxylic acids and derivatives of such acids containing at least one free carboxyl group. Reactions of this character are well known and take place vigorously resulting in character may be carriedwut in an aqueous medium provided suitable dispersing agents are employed for establishing an intimate contact between the reactants. The reaction conducted in accordance with the Hopfl et a1. patent requires from to 12 hours for completion but the patent states that the water present serves to effect 14 Claims. (01. 260-514) continuation input of copending application Serial No. 588,424, filed 1 April 14, 1945.

the withdrawal of the heat oi reaction and reduces dispersing agents, provided the pH concentration of the aqueous medium is maintained low and has a value below 7 and preferably below about 5. Our work indicates that the hydrogen ion promotes the reaction and is largely, if not wholly, responsible for the speeding up and completion of the reaction in aqueous media.

Copending application Serial No. 588,424 is didienes and 1,2 unsaturated carboxylic acids may be carried out quickly and in a manner to obtain substantially quantitive yields of relatively pure products.

A particular object of our invention is to provide methods for conducting such reactions wherein the pH value is maintained below '7 and preferably below about 5.

These and other objects and features of our invention will appear from the following description thereof wherein reference is made to specific exampleswhich have been cited for the purpose of indicating the nature of our invention but without intending to limit the scope of our invention thereby.

Processes which can be carried out in accordance with our invention may be generally represented by the following equations:

A. /g,, /0\ I o 0-0001: o 0-0 OOH -coon -coon o o and 0 0-0001: 0 \C--CO0H -e d g-ooon --coonwhere a is -c'-.

1,2 unsaturated organic acid compounds as a class, and including the mono-salts and esters of dicarboxylic acids, dicarboxylic acids as a class, such, for example, as maleic, itaconic, citraconic,

, mesaconic acids and the like, and their halogen rected particularly to, methods for treating waste liquors containing maleic acid or other unsaturated organic compounds, whereas the present invention relates generally to methods whereby conjugated dienes are reacted with 1,2 unsaturated carboxylic acids in the presence of a polar solvent and while maintaining the pH value below 7 and preferably below about 5.

The principal object of our invention is to provide novel methods for conducting reactions between conjugated dienes and 1,2 unsaturated carboxylic acids in the presence of a polar solvent. Another object of our invention is to provide methods whereby reactions between coniugated derivatives; also acrylic acid, water-soluble esters of acrylic acid and the like. Further by way of illustration the process is described in said copending applicationas employed in the treatment of aqueous waste liquors containing low concentration of maleic acid, in particular, the liquor resulting from the production of phthalic anhydride by oxidation. The reaction in general appears to take place when using any organic referred to as 1,2 unsaturated carboxylic acids.

Further, the reaction is general in that the 3 conjugated diene employed in the process may be any conjugated alicyclic (homocyclic) diene as a class such, for example, as cyclopentadienel,3; 1,3,5,5-tetramethyl cyclohexadiene-1,3 and the like; also oxygen-heterocyclic 1,3, dienes as a class such, for'example, as furan, furoic acid, cumalin, 2-methyl cumalin, sylvan (2-methyl furan) and the like; also aliphatic dienes as av class such, for example, as butadiene, isoprene, cyclohexadlene 1,3, alpha phellandrene and the like. The diene does not haveto be in the pure state but may be present in organic or inorganic mixtures or organic liquids and mayitself be a waste material, I I

Although the conjugated dienes are organic substances which are, in general, immiscible with is dependent upon the hydrogen ion concentration of the medium in which the reaction is-carried out. This is evident from the fact that the change in speed of reaction with change in the hydrogen ion concentration follows very closely the change i i-hydrogen ion concentration on titration of an aqueous solution of the unsaturated acid employed in forming. the reaction product. Thus in conducting reactions between maleicracid and cyclopentadiene in'an aqueous solution having a pH value of 0.71 the formation of the precipiwater, theywill react with the unsaturated com-,

pheric, for example, up to 5 atmospheres, the reaction is facilitated. In general, the diene is used in a mole equivalent of the unsaturated compound in the aqueous medium, but preferably the diene is used in -a slight excess of the theoretical amount.

The mixing of the diene with the vaqueous liquid is facilitated by the presence of a small amount, e. g. from 0.1% to 5% of a wetting agent in the reaction mixture. However, this is not necessary and in many commercial applications it is not even desirable. When a surface tension depressant is employed it is preferable to add it to the aqueous liquor before bringing'the diene into contact therewith. Suitable agents are, for example, sulfonated fatty acids, sulfated fatty alcohols, e. g. -Tergitol," ethylene oxide condensates of higher alcohols, e. g. Emulfor-O, Turkey-red oil and the like. As an alternative, the conjugated water-immiscible diene may be first emulsified with a small quantity e. g. from 2-20 times the weight of the diene of water (using a part of the polar solvent, water or waste liquor if desired). The emulsion is then added to the body of the solution containing the unsaturated carboxylic acid or to waste liquor to obtain an intimate mixing. Suitable emulsify-.

lng agents used for this purpose are, for example, soluble soaps, methyl cellulose, glue, gelatine and the like which may be used with wetting agents.

The products. resultin from the reactions de-. scribed may be considered to be alicyclic compounds because they contain only -one double bond and the other carbons of the ring are saturated. Referring to the typical equations cited above, the alicyclic acid I is obtained when the diene isaliphatic and the acid designated 11 is produced when .the diene used is cyclic. The acids thus obtained may be used per se or converted into the corresponding anhydrides, monoacidesters, and di-esters, or-converted by thermal decomposition back into maleic acid or the other unsaturated carboxylic acid employed in the reaction for use in the chemical and industrial arts.

The reactions-are exothermic and result in substantially quantitive yields of relatively pure products. However, the speed of the reaction in the presence of a polar solvent or aqueous medium tate is substantially instantaneous. A similar solution to which sodium'bicarbonate has been added until the pH value is 1.8 requires approximately 10 minutes to initiate the reaction and requires approximately 90 minutes for completion of the reaction during which time the pH valuerose to 4.28. Reactions in which the initial pH value is 6.0 take place so slowly as to be scarcely observable after vigorous shaking for V2 hour while reactions in which the pH value is 9.5 gave no indication of reaction whatever after vigorous shaking for 2 hours.

Moreover, it has been found that the neutral salts of maleic acid such, for example, as disodium maleate, wherein both '-COOH groups thereof have been reacted, do not react in non-alkaline polar type solvent media with the dienes of the class described. Such dienes react only with said mono.- and polycarboxylic acids and compounds wherein there at least one unsubstituted -COOH group attached to the molecule of the 1,2 unsaturated group and in the presence of an aqueous medium or polar solvent they react only within a non-alkaline pH range of not over 7.0.

The term "polar type solvent as employed herein is used in its ordinary sense; i. e., that type of solvent which will conduct a current when an ionizable compound is placed in thesolvent. Polar type solvents are often termed oxygenated solvents" because they ordinarily have oxygen present in the molecule, and comprise such solvents as water, alcohols, ethers, esters and the Example I 50 grams of maleic anhydride were introduced into a vessel containing 750 cc. of methyl alcohol at room temperature. No catalyst was present. A slow even reaction immediately took place between the alcohol and the maleic anhydride.

There was thus formed a monomethyl ester of maleic acid in an excess of alcohol. After reaction had been completed the solution had a pH value of 2,1. To this solution there was added 55 grams of cyclopentadiene whereupon reaction took place promptly forming the addition compound having the formula:

will be given asuasu This addition product was easily separated 1 from the alcoholic solution by distilling off the methanol.

Alternatively, the excess methanol may be permitted to remain and act as a solvent and/or reaction medium for preparing the dimethyl ester. with the addition of H2804, NaHSOa or other suitable catalysts. It was found that if the pH was adjusted to above 7.0 during reaction between cyclopentadiene and the monomethyl leate, the reaction stopped and would not proceed. However, upon readjustment of the pH to below 7, preferably to below 4.3, the reaction wasreinitiated and proceeded to completion. The temperature during reaction, was found to be slightly above that of room'temperature and rose during reaction to about 30 (3., thus indicating that the reaction is exothermic.

Example 11 product which by melting point and analysis wasv shown-to be bicyclo (2,2,1) fi-heptene 2,3 dicar-- boxylic acid. The pH initially was about 1.0 but gradually raised as the reaction proceeded to a value of about 4.3, whereupon the reaction was foundto be substantially completed. The temperature of reaction was preferably that of room temperature or slightly thereabove, but was not permitted to exceed the boiling point of cyclopentadiene, or 44 C. at ordinary atmospheric pressures.

Example 111- To 100 grams ofa 20% aqueous maleic acid solution there was added grams of disodium maleate. The pH of this mixture was found to be 0.71. A molar excess of cyclopentadiene was then added. There was formed a white precipvalue of 1.8. At the end of 10 minutes the soluto be shaken for V2 hour before there was apitate which settled out of the solution. After reaction the pH was found to be 4.82.

Example IV Example V Sodium bicarbonate was added to a 20% aqueous solution of maleic acid which initially had a pH value of 0.4 to 0.45 producing a solution having a pH value of 1.28. When this solution was reacted with cyclopentadiene the reaction did not take place quite so promptly and there was a lag of about 10 minutes before the reaction was concluded. The final pH value of the solution was 4.16.

The experiment was repeated using suflicient sodium bicarbonate solution to give an initial pH w more, it was found that no reaction would taketion became perceptively warmer and had reached a total of 10 degrees at the end of 20 minutes. The reaction was completed at about the end of 1% hours and the final pH value was 4.28.

When suflicient sodium bicarbonate was added to give an initial pH value of 2.45 the solution had preciable rise in temperature, whereas when the initial pH value was increased to 6 by the addition of sodium bicarbonate there was no rise in temperature and no evidence of reaction after vigorous shaking for /3 hour.

Example VI To a vessel there was added 500 grams of an aqueous solution of crude maleic acid which had been obtained as a by-product from the oxidation of naphthalene in the preparation of phthalic anhydride. The purpose of this test was to determine the content of maleic acid in the crude solution treated. The pH value of the solution was about 0.75. To this there was added an excess of freshly distilled cyclopentadiene comprising about grams of said diene. The reaction between the maleic acid and the diene took place immediately and was completed rapidly givin a final pH value of 1.8. This low final pH value may have been due to the presence of other organic or inorganic acids which did not take part in the reaction. A tan slurry of crystals formed in the reaction mixture. The reaction was exothermic, and hence the vessel was cooled with ice water during reaction. The crystals were illtered off and dried. The reaction product 'was found to have a melting point of l'l2-1'l4 C., as compared with a melting point of 182 C. for the pure acid product. To obtain a purer reaction product the waste liquor was heated to boiling for approximately 15 minutes, filtered. and the filtrate then treated with activated charcoal and again filtered. The product was then reacted with cyclopentadiene and the resultant reaction product was found to be pure white and had a melting point of 182 C. The yield of the reaction product obtained indicated that the total amount of maleic acid in the aqueous solution was 114 grams. In other words the 500 gram sample submitted contained 22.8% maleic acid by weight.

Example VII To 50 grams of the monomethyl ester of maleic acid dissolved in methyl alcohol there was added 25 grams of butadiene which was in molar excess with respect to the maleic acid. The pH'of the solution of monomethyl ester of maleic acid before adding the butadiene was 2.1. The reaction took place between the butadiene and the monomethyl ester of maleic acid in aqueous medium initially at room temperature, but since the reaction is exothermic, the temperature rose as the reaction proceeded. However, it was noted that the rate of the reaction increased considerably when heated under pressure to a temperature of C. in the'presence of butadiene. Furtherplace between butadiene and monomethyl ester of maleic acid when'the pH was above 1.0, or when laced in non-polar type solvent media.

From the above examples it will be seen that reaction between a diene and the-unsaturated carboxylic acids of the class described as, for example, maleic acid, homologues or derivatives thereof, will take place only in polar type solvents when the pH is not above 7.0, preferably at a pH 1,2 unsaturated organic acids of the class described are useful as intermediary starting materials for forming other valuable chemical compounds having many industrial applications.

- Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

We claim:

1. A process for reacting conjugated dienes with 1,2 unsaturated aliphatic carboxylic acid which comprises the step of contacting the reactants in the presence of a polar solvent for a period not exceeding about 90 minutes while maintaining the pH value of the reaction mixture below 7.

2. A process for reacting conJugated dienes with 1,2 unsaturated aliphatic carboxylic acid which comprises the step of contacting the reactants in the presence of a polar solvent tor a period not exceeding about '90 minutes while maintaining the pH value of said medium between about 0.1 and 5.0.

3. A process for reacting conjugated dienes with maleic acid which comprises the step of contacting the reactants in the presence of a polar solvent for a period not exceeding about 90 minutes while maintaining the pH value of the reaction mixture below '7.

4. A process for reacting conjugated dienes with maleic acid which comprises the step of contacting the reactants in the presence of an aqueous medium for a period not exceeding about 90. minutes while maintaining the pH value of said medium below '7.

5. A process for reacting conjugated dienes with maleic acid which comprises the step of contacting the reactants in the presence oi an aqueous medium for a period not exceeding about 90 minutes while maintaining the pH value of said medium between about 0.1 and 5.0.

6. A method for reacting an aliphatic diene with a 1,2 unsaturated carboxylic acid which comprises the step of contacting the reactants in an aqueous medium for a period not exceeding about minutes while maintaining the pH value of the 00 which comprises the step or contacting the reactants in an aqueous medium for a period not exceeding about 90 minutes while maintaining the value of the medium between about 0.1 and 5.0.

8. A method for reacting an aliphatic diene with maleic acid which comprises the step of contacting the reactants in an aqueous medium for a period not exceeding about 90 minutes while main-. taining the pH value 01' the medium below '7.

9. A method for reacting an aliphatic diene with maleic acid which comprises the step 01' contacting the reactants in an aqueous medium for a period not exceding about 90 minutes while maintaining the pH value of the medium between 0.1 and 5.0.

10. A method for reacting cyclopentadiene with a 1,2 unsaturated aliphatic carboxylic acid which I comprises the step of contacting the reactants in f an aqueous medium tor a period not exceeding about 90 minutes while maintaining the pH value of the medium between about 0.1 and 5.0.

12. A method for reacting cyclopentadiene with maleic acid which comprises'the step of contacting the reactants in an aqueous medium for a period not exceeding about 90 minutes while maintaining the pH value of'the medium below 7.

13. A' method for reacting cyclopentadiene with maleic acid which comprises the step 01' contacting the reactants in an aqueous medium for a period not exceeding about 90 minutes while maintaining the pH value of the medium between abou 0.1 and 5.0.

14. The process comprising adding cyclopentadiene to an aqueous solution of maleic acid having a pH numerically not greater than 5.0 maintaining the reactants in contact for a period not exceeding about 90 minutes thus forming a water insoluble condensation product of said maleic acid and cyclopentadiene and separating said insoluble product from the reaction mixture.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,994,731 Diels et a1. r Jan. 23, 1934 2,262,002 Hopi! et al Nov. 11, 1941 2,275,385 Soday Mar. 3, 194 :2

- I FOREIGNPATENTS Number Country Date Great Britain Mar. 5, 1930 

